Diaphragm for electronic-optical phase lenses



Oct. 7, 1941. E. BRUCHE ET Al.

DIAPHRAGM FOR ELECTRONIC-OPTICAL PHASE LENSES Filed Oct. 26, 1938 unnwapaan/nunnwynnnun vgngnnnnnunnua agnnn/nnnrn/nuvnnnpnnaun wnnnnnyannna xL SC H WDC N TRE R MBR .M INM., mA

Patented Oct. 7, 1941 DIAPHBAGM FOR ELECTRONIC-OPTICAL PHASE LENSES Ernst Brche, Berlin-Reinickendorf, and Alfred Recknagel, Berlin, Germany, assignors to General Electric Company, a corporation o! New York Application In October 26, 1938, Serial N0, 237,140 Germany October 26, 1937 6 Claims. (CL 25o-27) This invention relates to electronic devices, and in particular, to transit time electron tubes in which there is provided a phase diaphragm for increasing the operational efdciency of such tubes.

There are known electronic tubes in which the charge carriers (electrons or ions) are moved under the action of electric or magnetic alternating fields in such a manner that their transit time plays an important part in the operation of the device. This is the case, for instance, if the time spent by the electron or ion passing through the tube is comparable with the time of oscillation of the alternating iield or is long in comparison thereto.

To these so-called transit time devices belong, i'r instance, the dynamic multipliers as used for the'ampliiication of a quantity of electrons with the aid of the secondary emission of electrons: the multiple accelerator for the generation of high velocity charge carriers, and the arrangements for inducing high-frequency oscillations. To the last-buteone group pertains, among other devices, the cyclotron, and to the last group the oscillation generators of Barkhausen-Kurz and `the magnetron.

lin which, the beam or ray is focused or dispersed by a lens, so focusing or dispersion of electrons can be accomplished in an alternating iield. This focusing or dispersion does not relate. however, iirst of all to the directions, but to the temporal succession of the electrons which can be -assembled in time sequence at one point by means of such a phase-lens. used in the transit time devices constitutes, according to the theory, such a phase-lens with variable focal length which oscillates between a collecting lens across a planoparallel plate and a dispersing lens and back again. The focal length depends upon the variation speed of the field strength. Thus, a phase lens may be dened as an electron lens having a sinusoidal varying focal length.

The alternating field as this invention. a control device able to interrupt the electron current synchronously with respect to the alternating potential of the phaselens.

It is, for instance, possible to attain with the aid of such a phase-diaphragm, a phase-lens which exerts its action only at a certain definite focal length. Under this circumstance the action on the electron ray is similar to an optical apertured diaphragm, being such that the interruptions causeI the ray to fall onto the lens only within such intervals of time at which the focal length of the lens oscillates only slightly around a predetermined value. In general, the phase-diaphragm'when employed in connection with transit time devices causes the electron ray to be interrupted synchonously with respect to the frequency of the alternating potential exciting the field and is brought, in this manner, into a phase suited to the alternating potential,

whereby the efciency of the transit time device will be increased.

'I'he invention is illustrated diagramatically and by way of example on the accompanying drawing, in which Fig. l shows in schematic form one arrangement of electrodes in accordance with the invention to provide a phase diaphragm: Fig. 2 shows a modiiication of the electrode structure shown in Fig. 1 which permits variation of the applied alternating potential; Fig. 3 shows a further modification oiy the embodiment of a phase lens shown in Fig. 1 in which electromagnetic elds are used; Fig. 4 shows a graphical representation of the potentials of the vvarious electrodes under operating conditions of the structure shown in Fig. 1; Fig. 5 shows a modiilcation oi.' the embodiment of the structure to the cathode I. The grid 4 lies on a negative potential (for instance 1000 volts) relatively to the grid 3, and besides an alternating potential having an amplitude oi', for instance, 550 volts is connected up to the electrodes I and 4.

Fig. 4 serves to illustrate the manner of action of the diaphragm. In this ilgure the potentials of all electrodes are represented relatively to the cathodes as functions of the time. 'I'he electron ray can pass through the grid 4 only if this latter has a positive potential relatively to the cathode l. This is the case, during the entire period of the alternating potential, only in the interval of time from t1 to t: in which the alternating potential passes through its upper crest value. In other words, the interruption of the electron beam takes place synchronously with respect to the alternating potential. In connection therewith it is desirable to keep the amplitude of the alternating potential constant.

While Fig. 1 shows a phase-diaphragm, in which the electrons in general leave the grid 4 with a potential energy which is small relatively to the amplitude of the alternating potential, Fig. 2 shows a modification in which the emission speed can have any desired magnitude. There are in this example, the three grid electrodes I, 4 and 5, of which 3 and 5 are conductively connected with one another. The potentials ot the electrodes are the same as has been stated with respect to Fig. 4. The interrupted electron beam has in this case an energy of 500 volts.

In Fig. 5 is shown how the interruption of an electron current by means of a phase-diaphragm can be effected also by a change of the direction of said current. In this diagram 5 denotes a pair of deecting plates, 1 is a diaphragm, and I another pair of plates arranged therebehind.

An alternating potential connected up to the plates 6 causes the electron beam to oscillate in front of the diaphragm. The beam can pass through the diaphragm only if the absolute amount of the alternating potential lies below a certain limit. The frequency of the interruption is, therefore, twice the frequency of the alternating potential. As the direction of the beam permitted to pass has, in general, been changed, the pair of deflection plates l has been provided which brings the beam back into its former direction.

Fig. 3 shows a phase-diaphragm, the manner of operation is the same as the manner of operation of the phase-diaphragm shown in Fig. 4, but instead of the pair of deilection plates 5 a pair of deflection coils 9 is provided which causes the change of the direction of the electron beam and thereby the periodic interruption of the same.

In the arrangements, shown in Figs. 5 and 3, the deflection member I or 9 and the diaphragm 1 can, furthermore, be so arranged with respect to one another that an electron current can pass through the apertured diaphram only if the alternating potential of the phase diaphragm passes through one of the crest values thereof. In this case an interruption would be brought about by a change of the direction synchronously with respect to the alternating potential of the phase-diaphragm.

Fig. 6 illustrates how the phase-diaphragm `may be used in connection with a dynamic multiplier. The multiplier by way of example, is connected for operation as an amplifier. In the glass-vessel 2li an indirectly heated cathode emits electrons. which, through a cylindrically shaped control electrode 22 enter the phase-diaphragm formed by three electrodes 23, 24, 25. The construction of this phase-diaphragm corresponds to that described in Fig. l. Electrode 23 is formed as a diaphragm and at the same time serves as anode. while electrodes 24 and 25 consist of grid structures. After the electrons have passed through the phase-diaphragm they impinge on one of the known dynamic multipliers, which in this case consists oi' electrodes 26, 21. 28 and a surrounding electromagnetic coil 29. 'I'he latter serves for the generation of a magnetic ileld in the direction of the axis of the glass-vessel.

The cathode 2| is connected with the tap 32 of a direct current source lll, while cylinder 22 is connected with tap 3l of the same direct current source and thus is negatively biased with respect to the cathode.

'I'he control-voltage to be amplified is impressed on the control-cylinder 22 from the input terminals 34 and by means of the impedance 35. 'I'he anode 23 and the grid-like electrode 24 both are connected with tap Il of the directcurrent source 30 and are grounded. They receive a positive potential with respect to the cathode of, by way of example, some volts. The alternating voltage of the phase-diaphragm, as represented in Fig. 4 for instance, is impressed on the phase-diaphragm by the source I5. A battery 4| is provided as a negative bias for electrode 25 with respect to'electrode 24. 'I'he phasediaphragm and its connection herewith in every detail correspond to those represented in Figs. 1 and 4.

In the electron multiplierl as well known in the art, there are arranged two cathodes 25, 21, the cylindrical electrode 28 and an electromagnetic coil 29. On the cathodes 2l, 21 by means of terrnlnals 31, is impressed an alternating voltage of high frequency. The terminals l1 being symmetrical with respect to ground, their mean potential is that of ground. 'Ihe alternating potential on electrodes 25 and 21 causes an alternating field between these electrodes, which as already described forms a phase-lens with temporally variable focal-distance. The magnetic ileld of coil 2! serves for the concentration of the electrons traversing within the swinging multiplier.

As well known to those skilled in the art, the principle of the multiplier is that primary electrons which enter the multiplier through diaphragm 26 impinge on cathode 21 at a suitable phase of the alternating neld, emit there secondary electrons, which now on their part in suitable phase impinge on the other cathode 2l, emit there secondary electrons and so forth. Thus the primary electrons are multiplied and the electron stream may be taken on on the auxiliary electrode 2l,

It is known that when primary electrons enter the multiplier through the diaphragm 2l in a continuous stream, only a fraction of the electrons impinge Ion cathode 21 at such a phase of the alternating potential that this fraction efl'ectively takes part at the multiplying process. The other electrons have been brought into the multiplier without any use they are superfluous and only withdraw energy from the oscillating ileld which energy cannot be employed.

According to the invention with the phasediaphragm there is accomplished that the electrons impinge on the cathode 21 only at suitable phases of the alternating voltage that only such electrons occur which effectively take part ln the multiplying process.

The multiplied electrons reach the auxiliary anode 28, which is positively biased by direct current source 40, and appear on impedance 38 as the amplied control potential, provided that the control potential is of substantial lower frequency than the alternating voltage of high frequency of the multiplier and the phase-diaphragm. The amplied voltage may be taken off at terminals 39. s

Of course, instead of the phase-diaphragm 23, 24 any other phase-diaphragm as represented in Figs, 2, 3 and 5 may be used.

It is advantageous for the purpose in view to supply the phase-diaphragm and the phase-lens with alternating potential from the same source. In that case, the phase-diaphragm interrupts the electron. current with double the frequency of the diaphragm potential, it is, however, necessary to make use of means for doubling the frequency or for dividing it into halves, in order to insure that the interruption takes place synchronously with the lens potential.

While in the above description, the effect of the phase-diaphragm upon electrons has been emphasized, it is a matter of fact that a diaphragm of the said type can serve also for the control of ion currents and can be used, for instance, in connection with a cyclotron operating with ions.

We claim:

1. A transit 'time electron device comprising means for producing a concentrated beam of electrons, electrode means for controlling the in- 3. A transit time electron device comprising means for producing a concentrated beam of electrons, electrode means for controlling the intensity of the produced beam of electrons by electrical signals, an electron phase lens, and an electrostatic phase diaphragm interposed between said beam producing means and said phase lens.

4. An electron device comprising means for producing a concentrated beam of electrons, electrode means for controlling the intensity of the produced beam of electrons by electrical signals, a dynamic secondary electron multiplier incorporating an electron phase lens positioned in register with said beam producing means, and an electron phase diaphragm interposed between said beam producing means and said multiplier.

5. An electron device comprising means for producing a concentrated beam of electrons, electrode means for controlling the intensity of the produced beam of electrons by electrical signals, a dynamic secondary electron multiplier incorporating an electron phase lens positioned in register with said beam producing means, an electrostatic electron phase diaphragm interposed between said beam producing means and said multiplier, and connection means adapted to supply electrons from said multiplier to an output circuit under the joint control of said phase lens and said phase diaphragm.

6. An electron device comprising means for producing a concentrated beam of electrons, electrode means for controlling the'intensity oi the produced beam of electrons by electrical signals, a dynamic secondary electron multiplier incorporating an electron phase lens and an output electrode positioned in register with said beam producing means, an electron phase diaphragm interposed between said beam producing means and said multiplier, an impedance connected to said output electrode, and means to derive output energy from across said impedance.

ERNST BRCHE. Amaru) RECKNAGEL. 

